1. Field of the Invention
Specifically, the present invention is a process to capture energy from available heat sources, heretofore not considered commercially attainable because of their low temperature levels. An indirect heat exchanger facilitates heat transfer from these low temperature sources to a refrigerating agent that enters the exchanger as a lower temperature sub-cooled liquid or saturated condition and exits it as a vapor. The vapor is then uniquely superheated to condition it for turbine expansion and to produce electricity in a connected generator.
Heat may be extracted from renewable energy sources such as solar heated water in tropical or desert areas, or from geothermal spots. Heat may be extracted from power plant condenser rejected heat or stack gas waste heat. Heat may be extracted from any available source, leaving the source at a lower temperature level.
This process can serve as a stand-alone plant or be integrated with a power plant to recover rejected heat from the plant's condenser and stack gas to significantly improve plant thermal efficiency. A conventional steam power plant using the Rankine Cycle rejects approximately 55% of the fuel heat input in the condenser and 10% from the stack, resulting in a plant thermal efficiency of 35-40%. This process can increase plant thermal efficiency up to 70%.
Another feature of this process includes its capability to produce a combination of electrical power and desalinated water, by including a unique steam flash tower with a top-mounted tube and shell condenser. Non-potable water such as sea or brackish water is introduced to the flash tower for vacuum distillation with the remaining water returned to its source at a lower temperature. The flashed steam is then condensed on the outside tube surfaces of the condenser to produce potable water and to maintain flash tower vacuum pressure. The steam heat of condensation is transferred to a refrigerating agent circulating inside the tubes to vaporize it and then produce electrical power as described above.
This process allows greater flexibility in new power plant location since it provides independence from a cooling water source. It is an economical replacement for a typical plant's cooling tower, which discharges rejected heat into the atmosphere, consumes large amounts of expensive water, and may create condensate drift problems. It would not be necessary for plants to return rejected heat in cooling water to its source, mitigating environmental bio-equilibrium problems. Plant seasonal load variations caused by changing cooling water or air temperatures are prevented since a consistently low water temperature is returned to the condenser all year. Alternately, greater plant revenues may be realized by selling condenser cooling water BTU's as a product.
Integrating this process with a Rankine cycle steam power plant can produce a significant increase in electrical output using the recovered rejected heat from the plant condenser. In addition, significant desalinated water output can be produced, which is environmentally friendly. Current desalination plants have high capital investments, high operating and maintenance costs, and leave a mark on the environment.
Retrofitting this process to existing plants can significantly increase plant thermal efficiencies, reduce fuel costs, and reduce stack emissions without adding air pollution equipment. Revenues can be generated from sales of electricity, desalinated water, or cooling water BTU's. Power output from less efficient plants can be proportionally reduced with corresponding credit for reductions in emission of pollutants and carbon dioxide (CO2), without requiring the addition of high cost pollution collection equipment. Receiving of operating permits, monitoring of water discharge temperature for limit violations or load reductions, water intake fouling problems, environmental bio-equilibrium impacts, and forced load reductions during peak summer demand seasons would no longer be issues. Power plant efficiency can significantly improve by returning the cooling water to the plant condenser at a lower temperature than it receives through existing cooling equipment, producing more power output.
2. Prior Art Description
Current power plants operating on the Rankine cycle primarily uses condenser cooling water from nearby sources and cooling towers to reject low temperature energy causing low plant thermal efficiencies. Dissipation of condenser rejected heat from power plants is an environmental issue and various other ideas have been discussed such as using irrigation canals and holding ponds. Prior art has not disclosed a process that efficiently uses low temperature water as an energy source on a commercial scale.
This disclosed process can be applied in geothermal power plants, resulting in significantly higher thermal efficiencies of about 50% rather than currently demonstrated efficiencies of 7 to 10%. Application in tropical or desert areas would provide essential resources and greater outputs would be realized from sea water heated solar ponds. The capacity factor for this renewable energy process would be significantly higher than demonstrated with wind or solar cell energy.
Other than hydropower and geothermal, prior art has not disclosed an economical system to produce large amounts of renewable, clean electricity in a compact source at more locations. This disclosure includes these attributes.